The present invention relates to the installation of cables, such as optical fibre units, wires, electrical cables or the like. More specifically, but not exclusively, the present invention relates to the blowing of fibre unit cables through pre-laid conduits.
Optical fibres are widely used within telecommunication systems for high-speed information transfer. A fibre unit, which could comprise a single optical fibre, or a bundle of optical fibres, is commonly installed into a protective optical conduit comprising optical fibre tubes, which have already been laid along the desired route, usually as a continuous span between convenient access points such as surface boxes or inspection chambers.
The conduits typically are made of plastic, each with a typical inner diameter of 3 to 6 mm or more, and are usually provided in a bundle comprising up to 24 or more tubes, which are held together within a protective outer sheath. Each fibre conduit tube can receive at least one fibre unit comprising one or more individual optical fibres. Large numbers of conduits—and bundles of conduits—are pre-installed across the access network and the distribution network between the local exchanges and the customer premises in a branching network system. With the advent of fibre to the premises (FTTP), the conduits will further extend to and into commercial and residential premises. Indeed it is a fundamental part of the push to FTTP in e.g. the UK that substantially all the network comprises optical fibre, extending from the core network to as many end customers as possible. To achieve this, optical fibre installation needs to be speedy, cost- and effort-efficient.
In the vast majority of cases, a dedicated path is described between two points with a single length of conduit tube. In an exceptional case, the conduit path may comprise a number of lengths of physically separate conduit tubes which are connecterised together in series with tube connectors. Choosing the correct conduit tube at the installation should in the normal case, result in the fibre unit emerging at the other end.
Problems however may arise which result in the fibre unit not reaching the correct destination. During installation, the operator is usually presented with a large number of conduit tubes, which could result in a mistake in identifying the correct conduit, especially if the operator is working in adverse conditions down a manhole or in poor lighting. This may be so even where conduits are coloured coded which helps to direct the operator to the correct conduit.
There is also the possibility that a conduit route is wrongly mapped in the records used by the operator so that one end of the conduit does not lead to the correct destination. Where the path comprises a number of tube lengths connectorised together in series, yet another problem may lie in broken connections between lengths of conduit tubes within the network, so that the fibre unit may get lost within the system during installation and never emerge at the destination. Yet another issue may be the possibility that the fibre unit, during installation, could be impeded by an imperfect connector or a tight bend or some other source of friction in the conduit, and again never emerge at the destination.
For any of these or other reasons, the fibre unit will emerge in the wrong place, or not at all. Add to that some uncertainty about the exact length of the conduit route down which the fibre unit is being installed, so that the operator cannot even accurately know in a timely manner when something has gone wrong.
One method of installing fibre units into the conduits is by pulling them through the conduits. However, the tension induced can cause damage to the fibre units and impair their operating performance. A known alternative method is the “blown fibre” technique whereby a compressed fluid such as compressed air is used to convey, or “blow”, a fibre unit along a conduit from one end.
Currently, installing fibre units using the blown fibre method requires at least two operators: one situated at the head end of the conduit, where during installation air and the fibre unit is installed into the mouth of the conduit, and one at the remote end of the conduit, where air and the fibre unit emerges from the mouth of the conduit. The second remote end operator is required because the remote end is often some distance away—up to a kilometer or more—from the head end. The operator at the head end is therefore unable to know the status of the remote end during an installation without a second operator located there.
The head end operator monitors and operates a fibre installation mechanism—known in the art as a “blowing head”—that feeds the optical fibre into the conduit and controls the supply of compressed air. He starts the process by directing air into the mouth of the head end conduit. If the air is directed into the correct conduit, the remote end operator will sense the arrival of the air with an air flow meter temporarily connected to the end of the conduit, or more simply by feeling the air flow exiting the conduit against his hand if the air flow is sufficiently high. He then communicates this to the head end operator by radio or other means, to confirm to the head end operator that he is applying air to the correct conduit. The head end operator then introduces the fibre unit into the conduit and blows it through to the remote end of the conduit, whereupon the remote end operator advises his colleague on its arrival. The head end operator then turns off the air supply and the blowing head, and the process is complete.
This process is labour-intensive as a minimum of two operators must work on a single installation. The head end operator needs to be skilled in the operation of the blowing head, while the remote end operator is required to alert his colleague to the status of the installation at the remote end.
Methods whereby a single operator at the head end of a conduit can detect the arrival of an optical fibre at the remote end of the conduit are known.
In the simplest method, the length of the conduit route is known, allowing the operator to know that the fibre has (probably) arrived at the remote end when the required length of fibre unit has been played out. This relies on the map record of conduit route being up to date and accurate, and presumes a completely smooth and obstruction-free conduit route. Neither of these can be guaranteed in practice.
Another known practice is to install at the remote end of the conduit a barrier of porous material such as an “airstone” which is placed at the remote end of the conduit, which will allow air through but which will stop further progress of the fibre unit. This cease in progress is detected by the blowing head which then stops further ingress. However even when the progress of the fibre has ceased, the operator at the head end cannot be certain that the fibre unit has reached the porous barrier at the end of the conduit, or if instead the fibre unit is caught on an obstruction at some point along the length of the conduit.
As described in WO9103756, a solution is to position a light source at the remote end of the conduit and a light detector is positioned at the head end. The arrival of the optical fibre at the remote end is indicated by the detection of light by the detector at the head end. One problem with this method is that an early, or “false”, indication of the arrival of the optical fibre may occur if stray light is inadvertently introduced into the conduit at a location between the head end and remote end, e.g. at an open inspection chamber. This method also relies on adequate light being coupled into the advancing end of the optical fibre to be detected by the detector, however the coupling process is inefficient and is further degraded in proportion to the length of the optical fibre due to normal attenuation properties, so this method may not be practicable on long lengths of optical fibre. A second method described in this document uses a previously installed optical fibre to create part of a light “circuit” with the blown optical fibre. This method is not suitable for installing the first optical fibre in a conduit. Furthermore, any previously installed fibre units may be carrying live traffic and so would not be available to use for the installation of additional fibres.
Another known method is to use a blowing head such as that described in WO/9812588, which is configured to stop driving the fibre unit when it senses that fibre movement within the conduit is slowing down or stopping owing to an obstruction. When used in conjunction with a sealed-off remote end, the fibre unit would stop moving when it reaches the destination end. However, as the sealed-off end is just one type of obstruction the fibre unit may encounter on the conduit route, this method fails to positively identify when the fibre unit has reached and emerged from the conduit at the remote end without travelling to the remote end for a visual inspection.
Accordingly, in a general aspect, the present invention provides methods and devices for aspects relating to the installation of cables such as fibre units into conduit tubes, in particular, allowing a single operator to operate substantially on his own to determine if air fed into a conduit is reaching its intended destination, and/or if and when the fibre unit fed into the conduit has reached its destination. The invention can be used where the operator has to choose one of a number of conduits, or where there is a single conduit but where it is desirable to unambiguously confirm that the air and fibre unit reaches the intended destination.
A first aspect of the invention provides a method, for use in connection with installing a cable into a conduit having a first end and a second end, of detecting whether air is flowing from the first end to the second end, the method including the steps of                providing a movement sensor within or proximate to the conduit;        providing an air flow into the conduit from the first end; and        detecting that the air flow disrupts the movement sensor, whereby an operator may determine that air is flowing to the second end.        
By using this method, the operator may determine if he has chosen the correct conduit tube to feed the air flow into, or if in spite of making the correct choice, the air is nonetheless not reaching the desired remote end. The movement sensor will be disrupted by the sensed air flow and in one embodiment the sensor comprises a rotating blade which rotational speed is increased when the air flow arrives. The movement sensor can be placed at any point along the tube which would provide an indication of air flowing to the remote end, although preferably the sensor will indicate that the air is flowing out from the remote end of the tube, so the sensor can be placed at the end of the tube. In a further embodiment of the invention, the fact that the air flow has been sensed at the remote end can be signalled back to the operator at the head end.
A second aspect of the invention provides a method, for use in connection with installing a cable into a conduit having a first end and a second end, of detecting whether the cable has arrived at the second end, the method including the steps of                providing a movement sensor within or proximate to the conduit;        driving the cable through the conduit from the first end towards the second end; and        detecting that the cable disrupts the movement sensor, whereby an operator may determine that air is flowing to the second end.        
By using this method, the operator can determine that the cable has arrived at the remote end of the conduit tube, when the advancing end of the cable disrupts the movement sensor. In one embodiment the sensor comprises a rotating blade which rotational speed is decreased when the air flow arrives. The movement sensor can be placed at any point along the tube which would provide an indication that the cable has arrived at the remote end, although preferably the sensor is placed at the end of the tube. In a further embodiment of the invention, the fact that the air flow has been sensed at the remote end can be signalled back to the operator at the head end, and the apparatus providing the air flow and/or the apparatus mechanically driving the fibre into the conduit can be automatically shut off.
The term “disrupt” is used in the present document to indicate that a device or sensor in some way has its movement or state changed. Thus it may be used to indicate either that a sensing device has increased its rotational speed (e.g. because of an increase in air flow) or has decreased its rotational speed (e.g. because a fibre has jammed the sensor).
A third aspect of the present invention provides a method for use in connection with installing a cable into a conduit having a first end and a second end, comprising the steps of    (i) detecting whether air is flowing from the first end to the second end using a method including the steps of:            providing a movement sensor within or proximate to the conduit;        providing an air flow into the conduit from the first end; and        detecting that the air flow disrupts the movement sensor, whereby an operator may determine that air is flowing to the second end; and            (ii) detecting the arrival of the cable at the second end using a method including the steps of:            providing a movement sensor within or proximate to the conduit;        driving the cable through the conduit from the first end towards the second end; and        detecting that the cable disrupts the movement sensor, whereby an operator may determine that air is flowing to the second end.        
By using this method, the operator can initially determine that the correct conduit tube has been selected and/or otherwise that air being fed in at the head end, is reaching the remote end as desired. Upon confirming this, the operator knows that the cable fed into the identified tube can be blown to the same destination remote end as the air flow. Cable is then fed into the tube, and the operator can further know when the cable arrives at the remote end so that the apparatus providing air flow and/or the mechanical driving force can be shut off.
A fourth aspect of the present invention provides a device for use in connection with installing a cable into a conduit having a first end and a second end comprising                a movement sensor configured to be disrupted by one or both of the air flow and arrival of the cable at the second end; and        detecting means for detecting the disruption of the movement sensor.        
This device can be installed at any point which would provide the operator with an indication that the air flow and/or the cable has arrived at the remote end of the tube. Preferably, the device is positioned at the remote end itself, and comprises a rotatable blade capable of being disrupted by an air flow and/or the advancing end of the cable. The device could further be configured to send a signal to the operator at the head end to indicate that the movement sensor has been disrupted, indicating either air flow or cable arrival. Means to detect the disruption of the movement sensor can be a light source and light receiver, which would detect that disruption of the movement sensor causes an intermittent light signal to be received by the light receiver, indicating air flow or cable arrival.